Composite conductive material, power storage device, conductive dispersion, conductive device, conductive composite and thermally conductive composite and method of producing a composite conductive material

ABSTRACT

A composite conductive material includes at least graphene-like exfoliated from a graphite-based graphite carbon material and a conductive material dispersed in a base material. The graphite-based carbon material has a rhombohedral graphite layer (3R) and a hexagonal graphite layer (2H), wherein a Rate (3R) of the rhombohedral graphite layer (3R) and the hexagonal graphite layer (2H), based on an X-ray diffraction method, which is defined by following Equation 1 is 31% or more: 
       Rate (3 R )= P 3/( P 3+ P 4)×100  (Equation 1)
 
     wherein
         P3 is a peak intensity of a (101) plane of the rhombohedral graphite layer (3R) based on the X-ray diffraction method, and   P4 is a peak intensity of a (101) plane of the hexagonal graphite layer (2H) based on the X-ray diffraction method.

TECHNICAL FIELD

The present invention relates to a composite conductive material, apower storage device, a conductive dispersion, a conductive device, aconductive composite, a thermally conductive composite and method ofproducing a composite conductive material.

BACKGROUND ART

In recent years, addition of various nanomaterials has been studied forpurposes of downsizing and weight saving in various fields. Inparticular, for problems of environments or resources, carbon materialssuch as graphene, CNT and fullerene have attracted attention as nonmetalnanomaterials. For example, a lithium-ion battery currently put topractical use has been improved in its capacity owing to an improvementof the active material itself. However, the capacity is significantlylower than its theoretical capacity, and further improvement has beendesired.

Regarding this matter, while acetylene black has been conventionallyused as a conductive assistant for lithium-ion batteries, novel highconductive materials such as a carbon nanofiber (VGCF (vapor growncarbon fiber): registered trademark) manufactured by Showa Denko K.K.have been studied in recent years to further improve electricalconductivity (Patent Literature 1: JP-A-2013-77475).

Further, a method of improving cycle characteristics (repetitionperformance) of a battery by directly coating a positive electrodeactive material with an electrical conductor and a method of producing ahigh-capacity and high-output lithium-ion battery by focusing attentiononion conductivity have been studied. (Patent Literature 2:JP-T-2013-513904), (Patent Literature 3: WO 2014/115669)

Furthermore, nanosizing of an active material itself for a lithium-ionbattery has been also studied in recent years. (Non-Patent Literature 5)

CITATION LIST Patent Literature

-   PTL 1: JP-A-2013-77475 (Paragraphs 0031-0039)-   PTL 2: JP-T-2013-513904 (Paragraph 0016)-   PTL 3: WO 2014/115669 (Paragraphs 0017, 0018)-   PTL 4: WO 2014/064432 (lines 4-9 on page 19)

Non Patent Literature

-   NPL 1: Structural Change of Graphite with Griding; authors: Michio    INAGAKI, Hisae MUGISHIMA, and Kenji HOSOKAWA; Feb. 1, 1973    (Received)-   NPL 2: Changes of Probabilities P1, PABA, PABC with Heat Treatment    of Carbons; authors: Tokiti NODA, Masaaki IWATSUKI, and Michio    INAGAKI; Sep. 16, 1966 (Received)-   NPL 3: Spectroscopic and X-ray diffraction studies on fluid    deposited rhombohedral graphite from the Eastern Ghats Mobile Belt,    India; G. Parthasarathy, Current Science, Vol. 90, No. 7, 10 Apr.    2006-   NFL 4: Classification of solid carbon materials and their structural    characteristics; Nagoya Institute of Technology; Shinji KAWASAKI-   NPL 5: Synthesis of LiCoO2 nanoparticles. The Micromeritics (52),    13-18, 2009. Hosokawa Powder Technology Research Institute. (ISSN:    04299051)-   NPL 6: The National Institute of Advanced Industrial Science and    Technology. Single-wall carbon nanotube/carbon fiber/rubber    composite material having thermal conductivity equal to that of    titanium (http://www.aist.go.jp/aist_j/press_release/pr2011/pr201110    06/pr20111006.html)

SUMMARY OF INVENTION Technical Problem

However, a fundamental solution to the capacity is not obtained by suchmethods as disclosed in Patent Literatures 2 and 3, and Non-PatentLiterature 5, and the problem, it seems, lies somewhere else. In orderto conduct electricity and the like between substances, they simply needto be bridged by an electrical conductive material, however, there isusually resistance in a contact part between a conductor and anelectrical conductive material. Further, a contact area is small betweencurved surfaces and there are many point contacts, which contribute toan increased contact resistance. It is essentially considered thatresistance becomes higher as the number of contact points increases.

If this is applied to a lithium-ion battery, a positive electrode activematerial and a conductive assistant (an electrical conductor) such asacetylene black and VGCF are in a spherical or string-like shape, i.e.,a curved shape, having a size of a nano- to micrometer range, thus manyconductive assistants are interposed between positive electrode activematerials, thereby creating many contact points. Hence, it is consideredthat the theoretical capacity is not achieved because of the contactresistance.

As described above, the theoretical capacity has never been achieved inany of Patent Literatures 1 to 3, or Non-Patent Literature 5.

On the other hand, as for thermal conductivity, it has been proposedthat a high thermal conduction sheet can be obtained by combining carbonfibers and CNT, used in a small addition amount (Non-Patent Literature6). However, in this method, in the same manner as described above, asubstance in a string-like shape makes a point contact with each other,therefore heat transfer resistance is generated in a similar manner asin electric conductivity. As a result, the effect is not as high asexpected.

Regarding this matter, while paying attention to lowering contactresistance and maximally exploiting the performance of a conductor,studies have been conducted on the use of graphene, which is aconductor, a planar substance, and a flexible carbon material.

There has been a problem that an amount of the graphene that isexfoliated is normally small by processing natural graphite without anytreatments. However, as a result of earnest studies, by carrying outpredetermined treatments to graphite serving as a source material, thereis obtained a graphite-based carbon material (a graphene precursor),from which graphene is easily exfoliated, the graphene being able to bedispersed at a high concentration or to a high degree.

A part or whole of the graphene precursor is exfoliated by ultrasonicwaves, stirring and kneading to produce a mixed material being“graphene-like graphite”, containing material from the grapheneprecursors to the graphene. A size, thickness, etc. of the graphene-likegraphite is not limited since they are variable depending on an additionamount, a process time, etc. of the graphene precursors, however, thegraphene-like graphite is preferably more flaked.

That is, in other words, the graphite-based carbon material (thegraphene precursor) is a type of graphite capable of being easilyexfoliated and dispersed as graphene-like graphite by existing stirringand kneading processes or devices.

Since the graphene-like graphite is excellent in conductivity, it isfound that, when it is used in a high dispersion state, for example, ina positive electrode of a lithium-ion secondary battery, a capacitythereof can be made close to its theoretical capacity.

The invention has been completed focusing on such problems, and anobject of the invention is to provide a composite conductive material, apower storage device, a conductive dispersion, a conductive device, aconductive composite, a thermally conductive composite, and a method ofproducing a composite conductive material which are excellent inconductivity.

Solution to Problem

In order to solve the aforementioned problems, the composite conductivematerial of the present invention comprises at least graphene-likegraphite exfoliated from a graphite-based carbon material and aconductive material dispersed in a base material,

the graphite-based carbon material characterized by having arhombohedral graphite layer (3R) and a hexagonal graphite layer (2H),wherein a Rate (3R) of the rhombohedral graphite layer (3R) and thehexagonal graphite layer (2H), based on an X-ray diffraction method,which is defined by following Equation 1 is 31% or more:

Rate (3R)=P3/(P3+P4)×100  Equation 1

wherein

P3 is a peak intensity of a (101) plane of the rhombohedral graphitelayer (3R) based on the X-ray diffraction method, and

P4 is a peak intensity of a (101) plane of the hexagonal graphite layer(2H) based on the X-ray diffraction method.

According to the features, the composite material is excellent inconductivity. This is because, it is speculated that, the graphene-likegraphite exfoliated from the graphite-based carbon material exists in aflake state, thus the graphene-like graphite makes a contact with thebase material and the conductive material in many regions. It is alsospeculated that this is because the graphene-like graphite is thin andeasily deformable, thus the contact is made as a plane contact.

The conductive material is characterized by being a microparticle in astring-like, straight chain-like, linear, or flake-like shape.

According to the feature, the microparticle is surrounded by thegraphene-like graphite, thus conductivity of the microparticle can besufficiently exerted.

The microparticle is characterized by having an aspect ratio of 5 ormore.

According to the feature, conductivity of the microparticle can befurther sufficiently exerted.

A weight ratio of the graphite-based carbon material to the conductivematerial is characterized by being 1/50 or more and less than 10.

According to the feature, conductivity of the microparticle can beefficiently exerted.

The base material is characterized by being an active material for abattery.

According to the feature, an electrode excellent in charging anddischarging characteristics can be obtained.

The active material is characterized by being an active material for apositive electrode.

According to the feature, a positive electrode excellent in charging anddischarging characteristics can be obtained.

The base material is characterized by being a polymer.

According to the feature, a composite conductive material excellent inelectric, thermal, and ion conductivity can be obtained.

The base material is characterized by being a material that isannihilated by vaporization and the like.

According to the feature, the graphene-like graphite can be uniformlydispersed in the conductive materials by dispersing the graphene-likegraphite using the base materials and then by annihilating the basematerials.

A power storage device, such as a primary battery, secondary battery,and a capacitor, is characterized by comprising the composite conductivematerial.

According to the feature, a power storage device excellent in powerstorage performance can be obtained.

A conductive dispersion, such as a conductive ink, a conductive paste,and a conductive slurry, is characterized by comprising the compositeconductive material.

According to the feature, a conductive dispersion excellent inconductivity can be obtained.

A conductive device, such as a transparent electrode, a transparentconductive film, a conductive circuit, and a substrate, is characterizedby being coated or printed using the conductive dispersion.

According to the feature, a conductive device excellent in conductivitycan be obtained.

A conductive composite for use in preventing electrification and staticelectricity, intercepting electromagnetic waves, and the like ischaracterized by comprising the composite conductive material.

According to the feature, a conductive composite excellent inconductivity can be obtained.

A thermally conductive composite, such as a heat sink and a heatradiation grease, is characterized by comprising the compositeconductive material.

According to the feature, a thermally conductive composite excellent inheat transfer characteristics can be obtained.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a figure which shows a crystal structure of graphite, where(a) refers to a crystal structure of hexagonal crystals, and (b) refersto a crystal structure of rhombohedral crystals.

FIG. 2 is a diagram which shows an X-ray diffraction profile of generalnatural graphite.

FIG. 3 is a diagram which illustrates a production apparatus A using ajet mill and plasma of Example 1.

FIG. 4 is a figure which illustrates a production apparatus B using aball mill and magnetron of Example 1, where (a) is a diagram whichillustrates a pulverizing state, and (b) is a diagram which illustratesa state where graphite-based carbon materials (precursors) arecollected.

FIG. 5 is a diagram which shows an X-ray diffraction profile of agraphite-based carbon material of Sample 5 produced by the productionapparatus B according to Example 1.

FIG. 6 is a diagram which shows an X-ray diffraction profile of agraphite-based carbon material of Sample 6 produced by the productionapparatus A according to Example 1.

FIG. 7 is a diagram which shows an X-ray diffraction profile of agraphite-based carbon material of Sample 1 indicating a comparativeexample.

FIG. 8 is a diagram which shows a dispersion-producing apparatus whichproduces a dispersion using a graphite-based carbon material as aprecursor.

FIG. 9 is a diagram which shows dispersing states of dispersionsproduced by using graphite-based carbon materials of Sample 1 indicatinga comparative example, and Sample 5 produced by the production apparatusB of Example 1.

FIG. 10 FIGS. 10(a) and (b) are TEM images of a graphite-based carbonmaterial (graphene) dispersed in a dispersion.

FIG. 11 is a figure which shows distribution states of a graphite-basedcarbon material dispersed in a dispersion which was produced using agraphite-based carbon material (precursor) of Sample 5, where (a) is adiagram which shows an average size distribution, while (b) is a diagramwhich shows a distribution of the number of layers.

FIG. 12 is a figure which shows a distribution state of a graphite-basedcarbon material dispersed in a dispersion which was produced using agraphite-based carbon material of Sample 1 indicating the comparativeexample, where (a) is a diagram showing an average size distribution,and (b) is a diagram showing a distribution of the number of layers.

FIG. 13 is a diagram which shows distributions of the number of layersof graphite-based carbon materials each dispersed in dispersions thatwere produced using Samples 1 to 7 as precursors.

FIG. 14 is a diagram which shows proportions of graphene having 10layers or less to a content of rhombohedral crystals dispersed in adispersion.

FIG. 15 is a figure which shows a distribution state of graphite whenvarying conditions for producing a dispersion using a graphite-basedcarbon material (precursor) of Sample 5 according to Example 2, where(a) is a diagram showing a distribution in a case where an ultrasonictreatment and a microwave treatment were combined, while (b) is adiagram showing a distribution of the number of layers in a case wherean ultrasonic treatment was conducted.

FIG. 16 is a diagram which shows a resistance value when agraphite-based carbon material of Example 3 was dispersed in aconductive ink.

FIG. 17 is a diagram which shows a tensile strength when agraphite-based carbon material of Example 4 was kneaded with a resin.

FIG. 18 is a diagram which shows a tensile strength when agraphite-based carbon material of Example 5 was kneaded with a resin.

FIG. 19 is a figure which shows a distribution state of a graphite-basedcarbon material in a dispersion, dispersed in N-methylpyrrolidone (NMP),for providing a supplementary description of a dispersing state ofExample 5, where (a) is a distribution state of sample 12, and (b) is adistribution state of sample 2.

FIG. 20 is a graph which shows charging and discharging characteristicsof a lithium-ion secondary battery in Example 6, where (a) is a graphrepresenting Examples 6-1 to 6-3 and Comparative Examples 6-1 and 6-2,and (b) is a graph representing Comparative Example 6-3.

FIG. 21 is a conceptual drawing which shows a positive electrode of alithium-ion secondary battery in Example 6.

FIG. 22 is a SEM photographed image (plan view) of a graphene precursor.

FIG. 23 is a SEM photographed image (side view) of a graphene precursor.

FIG. 24 is a graph which shows charging and discharging characteristicsof a lithium-ion secondary battery in which carbon nanotubes are addedin Example 7.

FIG. 25 is a graph which shows charging and discharging characteristicsof a lithium-ion secondary battery in which a mixture ratio of agraphene precursor is changed in Example 8.

FIG. 26 is a SEM photographed image (cross-section view) of a resin inwhich graphene-like graphite is dispersed.

FIG. 27 is a SEM photographed image (side view) of the graphene-likegraphite in FIG. 26.

FIG. 28 is a schematic view which illustrates a shape of conductivematerials in Example 11, where (a) illustrates a shape of acetyleneblack, (b) illustrates a shape of a carbon fiber, and (c) illustrates ashape of a metallic particle.

DESCRIPTION OF EMBODIMENTS

The invention focuses on a crystal structure of graphite, and, at first,matters relating to the crystal structure will be explained. It has beenknown that natural graphite is classified into three types of crystalstructures, namely hexagonal crystals, rhombohedral crystals anddisordered crystals, depending on an overlapping manner of layers. Asshown in FIG. 1, hexagonal crystals have a crystal structure in whichlayers are arranged in the order of ABABAB . . . , while rhombohedralcrystals have a crystal structure in which layers are arranged in theorder of ABCABCABC . . . .

In natural graphite, there are almost no rhombohedral crystals in astage where natural graphite is excavated. However, about 14% ofrhombohedral crystals exist in general natural graphite-based carbonmaterials because pulverization or the like is carried out in apurification stage. In addition, it has been known that a proportion ofrhombohedral crystals converges on about 30% even when pulverization iscarried out during purification for a long time (Non-Patent Literatures1 and 2).

Moreover, a method in which graphite is expanded by heating, rather thanwith physical forces such as pulverization, thereby flaking thegraphite. However, even when graphite is treated with a heat of 1600 K(about 1,300° C.), a proportion of rhombohedral crystals is about 25%(Non-Patent Literature 3). Furthermore, the proportion is up to about30% even when heat of an extremely high temperature of 3000° C. isapplied thereto (Non-Patent Literature 2).

Thus, although it is possible to increase a proportion of rhombohedralcrystals by treating natural graphite with physical forces or heat, theupper limit is about 30%.

Hexagonal crystals (2H), which are included in natural graphite at ahigh level, are very stable, and an interlayer van der Waals' forcebetween their graphene layers is shown by Equation 3 (Patent Literature4). By applying an energy exceeding this force, graphene is exfoliated.An energy required for the exfoliation is inversely proportional to thecube of the thickness. Therefore, in a thick state where numerous layersare overlapped, graphene is exfoliated by a weak physical force such asby very feeble ultrasonic waves. However, in a case where graphene isexfoliated from somewhat thin graphite, a very large energy is required.In other words, even if graphite is treated for a long time, only weakparts of the surface are exfoliated, and large parts remain notexfoliated.

Fvdw=H·A/(6π·t ³)  Equation 3

Fvdw: Van der Waals' force

H: Hamaker constant

A: Surface area of graphite or graphene

t: Thickness of graphite or graphene

The present inventors succeeded in increasing a proportion ofrhombohedral crystals (3R), which had been increased to only about 30%by treatments of pulverization or heating to an extremely hightemperature, to 30% or more by carrying out predetermined treatments, asshown below, to natural graphite. The following findings were obtainedas results of experiments and studies. That is, when a content ofrhombohedral crystals (3R) in a graphite-based carbon material ishigher, particularly when the content is 31% or more, there is atendency that graphene is easily exfoliated by use of such agraphite-based carbon material as a precursor, thereby easily obtaininga highly concentrated and dispersed graphene dispersion or the like. Forthe reason, it is considered that, when a shear force or the like isapplied to rhombohedral crystals (3R), a deformation occurs betweenlayers, i.e. a deformation in the entire structure of the graphitebecomes large, and graphene is easily exfoliated independently of thevan der Waals' force. Accordingly, in the invention, a graphite-basedcarbon material, from which graphene is easily exfoliated by carryingout predetermined treatments to natural graphite, and which makes itpossible to disperse graphene at a high concentration or to a highdegree, is called a graphene precursor. Hereinafter, a method ofproducing a graphene precursor showing predetermined treatments, acrystal structure of the graphene precursor, and a graphene dispersionusing the graphene precursor will be described in that order in examplesbelow.

Here, in the specification, a graphene refers to a flake-like orsheet-like graphene which is a crystal of a mean size of 100 nm or morebut which is not a fine crystal of a mean size of several nanometers totens of nanometers, and which has 10 layers or less.

Additionally, since graphene is a crystal with a mean size of 100 nm ormore, when artificial graphite and carbon black, which are amorphous(microcrystal) carbon materials other than natural graphite, are eventreated, graphene cannot be obtained (Non-Patent Literature 4).

Further, in the specification, a graphene composite means a compositewhich is produced by using the graphite-based carbon material useful asa graphene precursor according to the invention, i.e. a graphite-basedcarbon material having a Rate (3R) of 31% or more (e.g. Samples 2-7 ofExample 1, samples 2, 21, . . . of Example 5 described below).

Hereinafter, examples for carrying out the composite conductivematerial, the power storage device, the conductive dispersion, theconductive device, the conductive composite, and the thermallyconductive composite, according to the present invention, will bedescribed.

Example 1 <As to Production of a Graphite-Based Carbon Material Usefulas a Graphene Precursor>

A method for obtaining a graphite-based carbon material useful as agraphene precursor by a production apparatus A using a jet mill andplasma shown in FIG. 3 will be explained. As an example, the productionapparatus A refers to a case in which plasma is applied for theradiowave-force-based treatment and in which the jet mill is used forthe physical-force-based treatment.

In FIG. 3, the symbol 1 refers to a particle of 5 mm or less of anatural graphite material (flaky graphite ACB-50 manufactured by NipponGraphite Industries, ltd.); the symbol 2 refers to a hopper which storesthe natural graphite material 1; the symbol 3 refers to a Venturi nozzlewhich discharges the natural graphite material 1 from the hopper 2; thesymbol 4 refers to a jet mill which jets the air which has been pumpedfrom a compressor 5, while being divided into eight places, to therebyallow the natural graphite material to collide against the inside of achamber by a jet blast; and the symbol 7 refers to a plasma generatorwhich sprays a gas 9, such as oxygen, argon, nitrogen or hydrogen,through a nozzle 8 from a tank 6 and which applies a voltage to a coil11, wound around the outer periphery of the nozzle 8, from ahigh-voltage power supply 10, thereby generating plasma inside thechamber of the jet mill 4, and the plasma generator is provided in eachof four places inside the chamber. The symbol 13 refers to a pipe whichconnects the jet mill 4 and a dust collector 14 to one another; thesymbol 14 refers to a dust collector; the symbol 15 refers to acollection container; the symbol 16 refers to a graphite-based carbonmaterial (graphene precursor); and the symbol 17 refers to a blower.

Next, the production method will be explained. Conditions for the jetmill and plasma are as follows.

The conditions for the jet mill are as follows.

Pressure: 0.5 MPa

Air volume: 2.8 m³/min

Nozzle inner Diameter: 12 mm

Flow rate: about 410 m/s

The conditions for plasma are as follows.

Output: 15 W

Voltage: 8 kV

Gas species: Ar (purity 99.999 vol %)

Gas flow rate: 5 L/min

It is considered that the natural graphite materials 1, which have beencharged into the chamber of the jet mill 4 from the Venturi nozzle 3,are accelerated to the sonic velocity or higher inside the chamber, andare pulverized by impact between the natural graphite materials 1 or byimpact of them against the wall, and that, simultaneously, the plasma 12discharges an electric current or excites the natural graphite materials1, acts directly on atoms (electrons), and increases deformations ofcrystals, thereby promoting the pulverization. When the natural graphitematerials 1 turn into fine particles of a certain particle diameter(about 1 to 10 μm), their mass is reduced, the centrifugal force isweakened, and, consequently, the natural graphite materials 1 are pumpedout from the pipe 13 which is connected to the center of the chamber.

A gas including graphite-based carbon materials (graphene precursors),which have been flowed from the pipe 13 into a cylindrical container ofthe chamber of the dust collector 14, forms a spiral flow, and drops thegraphite-based carbon materials 16, which collide with the internal wallof the container, to a collection container 15 below, while an ascendingair current generates in the center of the chamber due to a taperedcontainer part of the downside of the chamber, and the gas is emittedfrom the blower 17 (so-called cyclone effects). According to theproduction apparatus A in this example, about 800 g of a grapheneprecursor from 1 kg of the raw materials, i.e. natural graphitematerials 1, is used. The graphite-based carbon material (grapheneprecursors) 16 was obtained (recovery efficiency: about 80%).

Next, based on the production apparatus B using a ball mill andmicrowaves shown in FIG. 4, a method for obtaining a graphite-basedcarbon material useful as a graphene precursor will be described. Theapparatus B refers to, as an example, a case where microwaves areapplied as the radiowave-force-based treatment and where a ball mill isused for the physical-force-based treatment.

In FIGS. 4 (a) and (b), the symbol 20 refers to the ball mill; thesymbol 21 refers to a microwave generator (magnetron); the symbol 22refers to a wave guide; the symbol 23 refers to a microwave inlet; thesymbol 24 refers to a media; the symbol 25 refers to particles of 5 mmor less of a natural graphite material (flaky graphite ACB-50manufactured by Nippon Graphite Industries, ltd.); the symbol 26 refersto a collection container; the symbol 27 refers to a filter; and thesymbol 28 refers to graphite-based carbon material (grapheneprecursors).

Next, the production method will be explained. Conditions for the ballmill and the microwave generator are as follows.

The conditions for the ball mill are as follows.

Rotational speed: 30 rpm

Media size: φ5 mm

Media species: zirconia balls

Pulverization time: 3 hours

The conditions for the microwave generator (magnetron) are as follows.

Output: 300 W

Frequency: 2.45 GHz

Irradiation method: Intermittent

1 kg of natural graphite carbon raw materials 25 and 800 g of media 24are charged into the chamber of the ball mill 20, the chamber is closed,and the mixture is treated at a rotational speed of 30 rpm for 3 hours.During the treatment, microwaves are irradiated intermittently (for 20seconds every 10 minutes) to the chamber. It is considered that themicrowave irradiation acts directly on atoms (electrons) of the rawmaterials, thus increasing deformations of the crystals. After thetreatment, media 24 are removed by the filter 27, and thus, powder ofabout 10 μm of graphite-based carbon materials (precursors) 28 can becollected in the collection container 26.

<As to an X-Ray Diffraction Profile of Graphite-Based Carbon Materials(Graphene Precursors)>

With reference to FIGS. 5 to 7, X-ray diffraction profiles and crystalstructures will be described with respect to graphite-based naturalmaterials (Samples 6 and 5) produced by the production apparatuses A andB, and the powder of about 10 μm of graphite-based natural materials(Sample 1: a comparative example) obtained by using only the ball millof the production apparatus B.

The measurement conditions for the X-ray diffraction apparatus are asfollows.

Source: Cu Kα ray

Scanning speed: 20°/min

Tube voltage 40 kV

Tube current: 30 mA

According to the X-ray diffraction method(horizontal-sample-mounting-model multi-purpose X-ray diffractometerUltima IV manufactured by Rigaku Corporation), each sample shows peakintensities P1, P2, P3 and P4 in the planes (100), (002) and (101) ofhexagonal crystals 2H and in the plane (101) of rhombohedral crystals3R. Therefore, these peak intensities will be explained.

Here, the measurements of X-ray diffraction profile have been used theso-called standardized values at home and abroad in recent years. Thishorizontal-sample-mounting-model multi-purpose X-ray diffractometerUltima IV manufactured by Rigaku Corporation is an apparatus which canmeasure X-ray diffraction profile in accordance with JIS R 7651:2007“Measurement of lattice parameters and crystallite sizes of carbonmaterials”. In addition, Rate (3R) is the ratio of the diffractionintensity obtained by the Rate (3R)=P3/(P3+P4)×100, even if the value ofthe diffraction intensity is changed, the value of Rate (3R) is notchanges. Means that the ratio of the diffraction intensity isstandardized, it is commonly used to avoid performing the identificationof the absolute value substance and its value does not depend onmeasurement devices.

As shown in FIG. 5 and Table 1, Sample 5 produced by the productionapparatus B, which applies a treatment with a ball mill and a microwavetreatment, had high rates of peak intensities P3 and P1, and a Rate (3R)defined by Equation 1 showing a rate of P3 to a sum of P3 and P4 was46%. Additionally, the intensity ratio P1/P2 was 0.012.

Rate (3R)=P3/(P3+P4)×100  Equation 1

wherein

P1 is a peak intensity of a (100) plane of the hexagonal graphite layer(2H) based on the X-ray diffraction method,

P2 is a peak intensity of a (002) plane of the hexagonal graphite layer(2H) based on the X-ray diffraction method,

P3 is a peak intensity of a (101) plane of the rhombohedral graphitelayer (3R) based on the X-ray diffraction method, and

P4 is a peak intensity of a (101) plane of the hexagonal graphite layer(2H) based on the X-ray diffraction method.

TABLE 1 Peak intensities [counts · deg] (2θ [°]) Hexagonal crystals 2H(100) 162 [P1] (42.33) Hexagonal crystals 2H (002) 13157 [P2] (26.50)Rhombohedral crystals 3R (101) 396 [P3] (43.34) Hexagonal crystals 2H(101) 466 [P4] (44.57)

In the same manner, as shown in FIG. 6 and Table 2, Sample 6 produced bythe production apparatus A, which applies a treatment based on the jetmill and a treatment based on plasma, had high rates of peak intensitiesP3 and P1, and the Rate (3R) was 51%. In addition, the intensity ratioP1/P2 was 0.014.

TABLE 2 Peak intensities [counts · deg] (2θ [°]) Hexagonal crystals 2H(100) 66 [P1] (42.43) Hexagonal crystals 2H (002) 4,675 [P2] (26.49)Rhombohedral crystals 3R (101) 170 [P3] (43.37) Hexagonal crystals 2H(101) 162 [P4] (44.63)

Furthermore, as shown in FIG. 7 and Table 3, Sample 1 indicating acomparative example produced with only the ball mill had a small rate ofa peak intensity P3, compared with Samples 5 and 6, and the Rate (3R)was 23%. In addition, the intensity ratio P1/P2 was 0.008.

TABLE 3 Peak intensities [counts · deg] (2θ [°]) Hexagonal crystals 2H(100) 120 [P1] (42.4) Hexagonal crystals 2H (002) 15,000 [P2] (26.5)Rhombohedral crystals 3R (101) 50 [P3] (43.3) Hexagonal crystals 2H(101) 160 [P4] (44.5)

Thus, Sample 5 produced by the production apparatus B of Example 1, andSample 6 produced by the production apparatus A of Example 1 had Rates(3R) of 46% and 51%, respectively, and it was shown that their Rates(3R) were 40% or more, or 50% or more, compared with the naturalgraphite shown in FIG. 2 and Sample 1 indicating a comparative example.

Next, graphene dispersions were produced using the above-producedgraphene precursors, and their easiness in exfoliation of graphene wasevaluated.

<As to Graphene Dispersions>

A method for producing a graphene dispersion will be explained withreference to FIG. 8. FIG. 8 shows, as an example, a case where anultrasonic treatment and a microwave treatment are combined in a liquidwhen a graphene dispersion is produced.

(1) 0.2 g of a graphite-based carbon material useful as a grapheneprecursor and 200 ml of N-methylpyrrolidone (NMP) which serves asdispersing medium are charged to a beaker 40.(2) The beaker 40 is put into a chamber 42 of a microwave generator 43,and an ultrasonic trembler 44A of an ultrasonic horn 44 is inserted intodispersing medium 41 from the upper direction.(3) The ultrasonic horn 44 is activated, and ultrasonic waves of 20 kHz(100 W) are continuously applied thereto for 3 hours.(4) While the above ultrasonic horn 44 is actuated, the microwavegenerator 43 is activated to apply microwaves of 2.45 GHz (300 W)intermittently (irradiation for 10 seconds every 5 minutes) thereto.

FIG. 9 refers to appearances of graphene dispersions produced in theabove-described way when 24 hours had passed.

Although a portion of the graphene dispersion 30 using Sample 5 producedby the production apparatus B was deposited, a product entirely showinga black color was observed. For this, it is considered that a largeportion of the graphite-based carbon materials used as grapheneprecursors are dispersed in a state where graphene is exfoliated fromthem.

In the dispersion 31 using Sample 1 indicating a comparative example,most of the graphite-based carbon materials were deposited, and it wasconfirmed that a portion thereof floated as a supernatant. From thefacts, it is considered that graphene was exfoliated from a smallportion thereof and that they floated as the supernatant.

Furthermore, the graphene dispersion produced in the above-described waywas diluted to an observable concentration, was coated onto a samplestage (TEM grid), and the grid was dried. Thus, the size and the numberof layers of graphene was observed in the captured image of atransmission electron microscope (TEM), as shown in FIG. 10. Inaddition, the grid coated with the diluted supernatant was used forSample 1. For example, in the case of FIG. 10, the size corresponds to amaximum length L of a flake 33, which was 600 nm, based on FIG. 10 (a).As for the number of layers, the end face of the flake 33 was observedin FIG. 10 (b), and overlapping graphene layers were counted, therebycalculating the number of layers as 6 layers (a portion indicated by thesymbol 34). In this way, the size and the number of layers were measuredwith respect to each flake (“N” indicates the number of flakes), and thenumbers of graphene layers and the sizes shown in FIGS. 11 and 12 wereobtained.

With reference to FIG. 11 (a), a particle size distribution(distribution of sizes) of thin flakes included in the graphenedispersion of Sample 5 (Rate (R3) of 46%) produced by the productionapparatus B of Example 1 was a distribution having a peak of 0.5 μm. Inaddition, in FIG. 11 (b), as to the number of layers, a distributionwhich had a peak in 3 layers and in which graphene having 10 layers orless were 68% was observed.

With reference to FIG. 12, a particle size distribution (distribution ofsizes) of thin flakes included in the dispersion of Sample 1 (Rate (R3)of 23%) of the comparative example was a distribution having a peak of0.9 μm. In addition, as for the number of layers, a distribution inwhich those having 30 layers or more occupied the greater portion and inwhich graphene having 10 layers or less were 10% was observed.

From the results, it was revealed that, when the product of Sample 5produced by the production apparatus B was used as a graphene precursor,a highly-concentrated graphene dispersion which contains plenty ofgraphene of 10 layers or less and which has excellent dispersibility ofgraphene can be obtained.

Next, with reference to FIG. 13, a relation between the Rate (3R) of thegraphene precursor and the number of layers in the graphene dispersionwill be described. Samples 1, 5 and 6 in FIG. 13 are those describedabove. Samples 2, 3 and 4 were produced by the production apparatus Bwhich carried out a treatment based on a ball mill and a microwavetreatment, and were graphene dispersions produced using grapheneprecursors which had been produced by making the irradiating time ofmicrowaves shorter than that for Sample 5. In addition, Sample 7 wasproduced by the production apparatus A which carried out a treatmentbased on a jet mill and a plasma treatment, and was a graphenedispersion produced by using a graphene precursor which had beenproduced by applying plasma of a higher output than that for Sample 6.

From FIG. 13, as to Samples 2 and 3 showing Rates (3R) of 31% and 38%,respectively, the distributions of the number of layers have peaks ataround 13 as the number of layers; that is, the shapes of thedistributions are close to that of a normal distribution (dispersionsusing Samples 2 and 3). As to Samples 4 to 7 showing Rates (3R) of 40%or more, the distributions of the number of layers have peaks at severalas the number of layers (thin graphene); that is, the shapes of thedistributions are those of a so-called log normal distribution. On theother hand, as to Sample 1 having a Rate (3R) of 23%, the distributionthereof has a peak at 30 or more as the number of layers (a dispersionusing Sample 1). That is, it is understood as follows: there is atendency that, in cases where the Rate (3R) reaches 31% or more, theshapes of the layer number distributions differ from those for caseswhere the Rate (3R) is less than 31%; and further, in cases where theRate (3R) reaches 40% or more, the shapes of the layer numberdistributions clearly differ from those for cases where the Rate (3R) isless than 40%. In addition, it can be understood that, as to proportionsof graphene of 10 layers or less, the Rate (3R) of the dispersion usingSample 3 is 38%, while the Rate (3R) of the dispersion using Sample 4 is62%, and that, when the Rate (3R) reaches 40% or more, a proportion ofgraphene of 10 layers or less rapidly increases.

From these facts, it can be considered that graphene of 10 layers orless are easily exfoliated in cases where the Rate (3R) is 31% or more,and that, as the Rate (3R) increases to 40%, 50% and 60%, graphene of 10layers or less are more easily exfoliated. In addition, focusing on theintensity ratio P1/P2, Samples 2 to 7 show values within a comparativelynarrow range of 0.012 to 0.016, and any of them are preferable becausethey exceed 0.01 where it is considered that graphene is easilyexfoliated since crystal structures will be deformed.

Furthermore, results obtained by comparing Rates (3R) and proportions ofgraphene of 10 layers or less included therein are shown in FIG. 14.With reference to FIG. 14, it was revealed that, when the Rate (3R)reached 25% or more, around 31%, graphene of 10 layers or less startedto increase (showing an ever-increasing slope). Further, it was revealedthat, around 40%, graphene of 10 layers or less rapidly increased (as toproportions of graphene of 10 layers or less, whereas the Rate (3R) ofthe dispersion using Sample 3 was 38%, the Rate (3R) of the dispersionusing Sample 4 was 62%, and the proportion of graphene of 10 layers orless rapidly increased by 24% as the Rate (3R) increased by 4%), andthat a percentage of graphene of 10 layers or less against the totalgraphene was 50% or more. In addition, the points of black squares inFIG. 14 each correspond to different samples, and above-describedSamples 1 to 7 and other samples are included therein.

From the facts, when a sample showing a Rate (3R) of 31% or more is usedas a graphene precursor to produce a graphene dispersion, the proportionof distributed graphene of 10 layers or less starts increasing; further,when a sample showing a Rate (3R) of 40% or more is used as a grapheneprecursor to produce a graphene dispersion, 50% or more of graphene of10 layers or less are produced. In other words, a graphene dispersion inwhich graphene is highly concentrated and highly dispersed can beobtained. Furthermore, because almost no graphite-based carbon materials(precursors) included in the dispersion deposit as described above, aconcentrated graphene dispersion can easily be obtained. According tothis method, even a graphene dispersion whose graphene concentrationexceeded 10% can be produced without concentrating it. Particularly, theRate (3R) is preferably 40% or more from a view point that theproportion of dispersed graphene of 10 layers or less sharply increasesto 50% or more.

The above description clarifies the following: when the Rate (3R) is 31%or more, preferably 40% or more, and further preferably 50% or more,separation into graphene of 10 layers or less and thin graphite-basedcarbon materials of around 10 layers occurs in a greater proportion inmany cases; and in the case where these graphite-based carbon materialsare used as graphene precursors, a highly-concentrated graphenedispersion that has excellent dispersibility of graphene can beobtained. Still further, Example 5 to be described below clarifies that,in the case where the Rate (3R) is 31% or more, graphite-based carbonmaterials are useful as a graphene precursor.

Furthermore, an upper limit for the Rate (3R) is considered that theupper limit is not particularly defined. However, it is preferable thatthe upper limit is defined such that the intensity ratio P1/P2simultaneously satisfies 0.01 or more, because graphene precursors areeasily exfoliated when a dispersion or the like is produced. Inaddition, in cases of production methods using production apparatuses Aand B, the upper limit is about 70%, from a viewpoint that graphene iseasily produced. Also, a method combining a treatment based on the jetmill of the production apparatus A and a plasma treatment is morepreferable, because a graphene precursor having a higher Rate (3R) caneasily be obtained. Additionally, the Rate (3R) as long as it reaches31% or more by combining the physical-force-based treatment and theradiowave-force-based treatment.

Example 2

In Example 1, a case where the ultrasonic treatment and the microwavetreatment were combined for obtaining a graphene dispersion isexplained. In Example 2, only an ultrasonic treatment was carried outwhile a microwave treatment was not carried out, and other conditionswere the same as those for Example 1.

FIG. 15 (b) shows a distribution of a number of layers with respect to agraphene dispersion which was obtained by carrying out an ultrasonictreatment using the graphene precursor of Sample 5 (Rate (3R)=46%)produced by the production apparatus B. In addition, FIG. 15 (a) is thesame as the distribution shown in FIG. 11 (b) of Sample 5 produced bythe production apparatus B of Example 1.

As a result, although the tendency of the distribution of the number oflayers was almost similar, a proportion of graphene of 10 layers or lesswas 64%, and was slightly decreased, compared with 68% of Example 1.From the fact, it was revealed that it was more effective tosimultaneously carry out two of the treatments based on a physical forceand a radiowave force for producing a graphene dispersion.

Example 3

In Example 3, an example used for a conductive ink will be described.

Sample 1 (Rate (3R)=23%), Sample 3 (Rate (3R)=38%), Sample 5 (Rate(3R)=46%) and Sample 6 (Rate (3R)=51%) of Example 1 were used asgraphene precursors in mixture solution of water and an alcohol of thecarbon number of 3 or less, which severed as a conductivity-impartingagent, at concentrations adopted for conductive inks, thus producingINK1, INK3, INK5 and INK6, and their resistance values were compared.Based on the results, as the Rates (3R) became higher, the resistancevalues were lower.

Example 4

In Example 4, an example in which a graphene precursor was kneaded witha resin will be explained.

When a resin sheet, in which graphene was dispersed, was produced, thetensile strength was very superior although glass fibers were addedthereto. Therefore, a factor for this was studied, and, consequently, afinding that a compatibilizer added simultaneously with the glass fiberscontributed to formation of graphene from the precursor could beobtained. Therefore, products obtained by mixing dispersing agents and acompatibilizer into a resin were studied.

1 wt % of Sample 5 (Rate (3R)=46%) of Example 1 was added as a precursordirectly to LLDPE (polyethylene), and the mixture was kneaded whileapplying shear (a shearing force) thereto with a kneader, two-shaftkneader (extruder) or the like.

It has been publicly known that, when a graphite-based carbon materialsturned into graphene, being highly dispersed in a resin, the tensilestrength increases. Therefore, by measuring a tensile strength of theresin, degrees of exfoliating into graphene and dispersion canrelatively be estimated. The tensile strength was measured with an exacttabletop general-purpose testing machine (AUTOGRAPH AGS-J) manufacturedby Shimadzu Corporation under a condition of test speed of 500 mm/min.

In addition, in order to compare degree of exfoliating into graphene anddispersibility depending on the presence or absence of additives, thefollowing comparisons of three types of (a), (b) and (c) were carriedout.

(a) No additives(b) a general dispersing agent (zinc stearate)(c) a compatibilizer (a graft-modified polymer)

With reference to FIG. 17 showing the measurement results, the resultswill be explained. In addition, in FIG. 17, circles refer to resinmaterials using Sample 1 of the comparative example, and squares referto resin materials using Sample 5 of Example 1.

In case (a) where no additive was added, a difference of the tensilestrengths was small.

In case (b) where the dispersing agent was added, it was revealed thatformation of graphene was promoted to a certain degree in the grapheneprecursor of Sample 5.

In case (c) where the compatibilizer was added, it was revealed thatthat formation of graphene was significantly promoted in the grapheneprecursor of Sample 5. This is because it is considered that, besideseffects to disperse graphene, the compatibilizer binds the graphenelayer-bound bodies and the resin, and acts on them such that thegraphene layer-bound bodies are stripped therefrom, when applying shearin that state.

Zinc stearate is explained above as an example of the dispersing agent.However, those suited for compounds may be selected. As examples of thedispersing agent, anionic (anion) surfactants, cationic (cation)surfactants, zwitterionic surfactants, and nonionic surfactants can bementioned. In particular, anion surfactants and nonionic surfactants arepreferable for graphene. Nonionic surfactants are more preferable. Sincenonionic surfactants are surfactants which do not dissociate into ionsand which show hydrophilic properties by hydrogen bonds with water, asobserved in oxyethylene groups, hydroxyl groups, carbohydrate chainssuch as glucoside, and the like, there is a merit that they can be usedin nonpolar solvents, although they do not have a strength ofhydrophilicity as high as ionic surfactants. Further, this is because,by varying chain lengths of their hydrophilic groups, their propertiescan freely be changed from lipophilic properties to hydrophilicproperties. As anionic surfactants, X acid salts (as for the X acid, forexample, cholic acid, and deoxycholic acid), for example, SDC: sodiumdeoxycholate, and phosphate esters, are preferable. Furthermore, asnonionic surfactants, glycerol fatty acid esters, sorbitan fatty acidesters, fatty alcohol ethoxylates, polyoxyethylene alkyl phenyl ether,alkyl glycosides, and the like are preferable.

Example 5

In order to further verify that those obtained when the Rate (3R) is 31%or more are beneficial as graphene precursors, which is described abovein Example 1, an example in which a graphene precursor was kneaded witha resin will be further explained in Example 5. The following explainselastic moduli of resin molded articles in which graphite-based carbonmaterials containing Samples 1 to 7 in Example 1, having Rates (3R)plotted in FIG. 14, were used as precursors.

(1) Using the above-described graphite-based carbon material as aprecursor, 5 wt % of LLDPE (polyethylene: 20201) produced by PrimePolymer Co., Ltd.) and 1 wt % of a dispersant (nonionic surfactant) weremixed in an ion-exchanged water, and the above-described deviceillustrated in FIG. 8 was actuated under the same conditions, wherebygraphene dispersions containing 5 wt % of graphene and graphite-basedcarbon materials were obtained.

(2) 0.6 kg of the graphene dispersion obtained in (1) was immediatelykneaded into a resin of 5.4 kg using a kneader (pressing-type kneaderWDS7-30 produced by Moriyama Co., Ltd.), whereby pellets were produced.The kneading conditions are to be described below. It should be notedthat the mixing ratio between the resin and the dispersion was selectedso that the amount of the graphene and graphite-based carbon materialsmixed therein was eventually 0.5 wt %.

(3) The pellets produced in (2) were formed into a test piece accordingto JIS K7161 1A (length: 165 mm, width: 20 mm, thickness: 4 mm) by aninjection molding machine.

(4) The elastic modulus (Mpa) of the test piece produced in (3) wasmeasured under a condition of a test speed of 500 mm/min according toJIS K7161 by a table-top type precision universal tester produced byShimadzu Corporation (AUTOGRAPH AGS-J).

The kneading conditions were as follows.

Kneading temperature: 135° C.

Rotor rotation speed: 30 rpm

Kneading time: 15 minutes

Pressurization in furnace: applying 0.3 MPa for 10 minutes after start,and depressurizing to atmospheric pressure after the 10 minutes elapsed

Here, the dispersion of the above-described graphene dispersion into aresin is considered as follows. As the melting point of a resin isgenerally 100° C. or higher, water evaporates in atmosphere, but in apressing-type kneader, the inside of a furnace can be pressurized. Inthe inside of the furnace, the boiling point of water is raised so thatthe dispersion is kept in a liquid form, whereby an emulsion of thedispersion and the resin can be obtained. After applying pressure for apredetermined time, the inside is gradually depressurized, which causesthe boiling point of water to decrease, thereby allowing water toevaporate. Here, graphene confined in water are left in the resin. Thiscauses graphene and graphite-based carbon materials to be dispersed at ahigh concentration in the resin.

Further, since the graphene and graphite-based carbon materials tend toprecipitate in the graphene dispersion as time elapses, the graphenedispersion is kneaded into the resin preferably immediately after thegraphene dispersion is obtained.

It should be noted that the following may be used as the means forobtaining the emulsion of the dispersion and the resin, other than thepressing kneader: a chemical thruster; a vortex mixer; a homomixer; ahigh-pressure homogenizer; a hydroshear; a flow jet mixer; a wet jetmill; and an ultrasonic generator.

Further, the following may be used as a solvent for the dispersion,other than water: 2-propanol (IPA); acetone; toluene;N-methylpyrrolidone (NMP); and N,N-dimethyl formamide (DMF).

Table 4 illustrates the relationship between the Rates (3R) of around30% and the elastic moduli of resin molded articles. It should be notedthat Sample 00 in Table 4 is a blank Sample in which no precursor waskneaded, Samples 11 and 12 have Rates (3R) between that of Sample 1 andthat of Sample 2, and Sample 21 has a Rate (3R) between that of Sample 2and that of Sample 3.

TABLE 4 Sample No. 00 1 11 12 2 21 3 4 P3/(P3 + P4) — 23% 25% 28% 31%35% 38% 42% Elastic 175 197 196 199 231 249 263 272 modulus (MPa)(Average in 5 times) Difference — 12.4%  12.0%  13.9%  31.7%  42.1% 50.0%  55.6%  from blank Under-10 — 10% 12% 25% 25% 30% 38% 62% layersupon dispersion in NMP (Reference)

FIG. 18 and Table 4 prove that the difference of the elastic moduluswith respect to that of Sample 00 (blank) (increase ratio of the elasticmodulus) is approximately uniform around 10% until the Rate (3R) reaches31%; after the Rate (3R) reaches 31%, the difference sharply increasesto 32%; while the Rate (3R) increases from 31% to 42%, the differencemonotonously increases to 50%; and after the Rate (3R) reaches 42%, thedifference slightly increases and converges to around 60%. In this way,when the Rate (3R) is 31% or more, a resin molded article having anexcellent elastic modulus can be obtained. Further, since the amount ofgraphene and graphite-based carbon materials contained in a resin moldedarticle is 0.5 wt %, which is small, influence on properties that theresin originally possesses is small.

It is considered that this tendency attributes to a sharp increase in athin graphite-based carbon material containing graphene having 10 orless layers in contact with a resin after the Rate (3R) reaches 31%.Here, in Example 5, it is impossible to determine the number of layersof graphene by observation with TEM due to influences of a dispersantused for dispersion in water. Then, only for reference, the reason forthe sharp increase described above is considered based on thedistribution of the numbers of layers of the graphite-based carbonmaterial illustrated in Table 4 upon dispersion in NMP. Sample 12 andSample 2 are compared with each other, and it is found that both of theproportions of graphene (the number of layers are 10 or less) were 25%.On the other hand, as illustrated in FIG. 19, as to Sample 2, theproportion of thin ones having less than 15 layers was greater ascompared with Sample 12; in other words, the graphite-based carbonmaterial dispersed as a precursor had a larger surface area, which meansthat the area thereof in contact with the resin sharply increased.

In this way, Example 5 clearly indicates that when the Rate (3R) is 31%or more, a graphite-based carbon material used as a graphene precursortends to be separated into graphene having 10 or less layers and a thingraphite-based carbon material.

Example 6

Experiments were performed to obtain a positive electrode of alithium-ion secondary battery using the graphene precursor produced bythe above methods.

<Various Conditions>

Solvent: NMP (N-methylpyrrolidone) (battery grade manufactured byMitsubishi Chemical Corp.),

Conductive assistant (conductive material): Acetylene black (HS-100manufactured by Denki Kagaku Kogyo Kabushiki Kaisha, average particlediameter of 48 nm, bulk density of 0.15 g/ml, ash content of 0.01%),

Graphite-based carbon material: Graphene precursor (produced by abovemethod),

Binding agent: PVdF (PolyVinylidene) (SolefTA5130 manufactured bySolvay),

Positive electrode active material (base material): NCM Li(Ni_(1/3),Co_(1/3), Mn_(1/3))O₂) manufactured by Mitsui Mining & Smelting Co.,Ltd. (average particle diameter of 30 μm),

Ultrasonic treatment device (UP100S manufactured by HielscherUltrasonics GmbH),

-   -   <Treatment condition: 20 kHz, 100 W>    -   <Dispersion condition 1: Same as the preparing method of the        dispersion of the exfoliated graphene precursors in Example 1        (FIG. 8). Applying conditions of ultrasonic waves and microwaves        are also the same.>

Mixer (ARE-310 manufactured by THINKY),

-   -   <Mixing condition 1: Normal temperature of 25° C., mixing at        2,000 rpm×10 min>    -   <Mixing condition 2: Normal temperature of 25° C., mixing at        2,000 rpm×10 min, defoaming after mixing at 2,100 rpm×30 sec>,

Separator (2400 manufactured by Celgard, LLC., plate thickness of 25 μm,material: PP (polypropylene)),

Electrolyte solution: EC (ethylene carbonate) containing 1.0 mol/L ofLiPF6 (lithium hexafluorophosphate):DEC (diethyl carbonate) (7:3 vol %)(manufactured by Kishida Chemical Co., Ltd.),

Lithium foil (negative electrode): (manufactured by Honjo Metal Co.,Ltd., thickness of 0.2 mm)

Experimental Procedures

Step 1. To NMP (90 g), 10 g of graphene precursors (see Samples 1, 2,21, and 4 (Samples used in Examples 1 and 5)) are added, and, under thedispersion condition 1, the graphene precursors are exfoliated anddispersed to obtain a dispersion of 10 wt % in concentration.Step 2. The dispersion (20 g), PVdF (4 g), and acetylene black (6 g) areadded and mixed under the mixing condition 1 to obtain a 30 g of mixture1.Step 3. To the mixture 1, positive electrode active materials are addedat a ratio shown in Table 5 and mixed under the mixing condition 2 toobtain a mixture 2.Step 4. The mixture 2 is coated on an aluminum foil to a film thicknessof 0.25 mm, and the coating material is vacuum-dried at 100° C. andpressed by a pressure of 1.5 MPa to obtain a positive electrode having agiven thickness.Step 5. The positive electrode is punched into a shape having a diameterof 15 mm.Step 6. The lithium foil is pressed and fixed to a stainless steel panelserving as a negative electrode, the separator, the electrolytesolution, and the positive electrode were overlaid in this order, andthe overlaid product was mounted on an HS cell made of stainless steelmanufactured by Hohsen Corp.Step 7. Electrochemical characteristic evaluation of the HS cell wasperformed under the following test conditions.

It should be noted that, in the above procedures, a transition to thenext step was performed successively without having a standby time. Thesame applied to the following examples.

<Test Conditions>

Initial charging: CC-CV charging 0.2 C (0.01 C cut off)Initial discharging: CC discharging 0.2 CAssembling environment: 25° C., a dew point of −64° C. under argonatmosphere (inside of a glove box)Voltage range: 2.75 V to 4.5 V vs. Li/Li+Measuring device: BTS2004W manufactured by Nagano Co., Ltd.

It is noted that CC-CV charging refers toconstant-voltage/constant-current charging and CC discharging refers toconstant-current discharging, while 0.2 C is a charge/discharge rate in5 hours and 0.01 C cut off represents a cut-off condition.

Further, in order to confirm an effect of graphene-like graphite,experiments were performed with a Rate (3R) of 23% (Sample 1), 31%(Sample 2), 35% (Sample 21), and 42% (Sample 4) having a mixture ratioshown in Table 5.

TABLE 5 Mixture ratio (wt %) Graphene precursor Rate (3R) = Rate (3R) =Rate (3R) = Rate (3R) = NCM AB PVdF 23% (Sample 1) 31% (Sample 2) 35%(Sample 21) 42% (Sample 4) Example 6-1 94 3 2 — 1 — — Example 6-2 94 3 2— — 1 — Example 6-3 94 3 2 — — — 1 Comparative 94 3 2 1 — — — example6-1 Comparative 95 3 2 — — — — example 6-2 Comparative 95 — 2 — 3 — —example 6-3

From Table 5 and FIG. 20, Examples 6-1, 6-2, 6-3, Comparative example6-1, and Comparative example 6-2 in which the graphene-like graphite wasnot dispersed indicated a similar trend in charging characteristic whencharging was conducted to a charging potential of 4.5 V at a rate of 0.2C. Examples 6-1, 6-2, and 6-3, especially Example 6-3 by comparison, aremore preferable since a charging voltage is quickly increased. Incontrast, a charge behavior failed to be observed in Comparative example6-3. It is speculated that this is because a conductive path couldn't beformed by nanoparticles such as the graphene-like graphite alone withouthaving materials in a string-like shape such as acetylene black.

Further, as for discharging characteristics, it was observed thatExamples 6-1, 6-2, and 6-3 had a higher charge end potential thanComparative examples 6-1 and 6-2. It was further observed that Examples6-1, 6-2, 6-3, and Comparative example 6-1, in all of which thegraphene-like graphite was dispersed, had a greater capacity thanComparative example 6-2, where the graphene-like graphite was notdispersed. It was observed that the capacity is significantly increasedespecially in Examples 6-1, 6-2, and 6-3. On the other hand, a dischargebehavior failed to be observed in Comparative example 6-3.

By using the graphene-like graphite exfoliated from the grapheneprecursors having the Rate (3R) of 31% or more (Examples 6-1, 6-2, and6-3) together with AB, it was confirmed that a resulting batteryexhibited a high charge end potential and was excellent in thedischarging characteristic of a positive electrode. Especially, fromFIG. 20, it was confirmed that the charge end potential showed atendency to increase sharply after the Rate (3R) reached 31%. It isspeculated that, as shown in FIG. 21, between positive electrode activematerials 52 and 52, having a particle diameter of several tens of μm,there exist conductive assistants AB53, 53, . . . 53, formed in astring-like shape, having a cross sectional diameter of several tens ofnm, and that graphene-like graphite 54 (e.g., a thickness of 50 nm orless, a size of 100 nm to 5 μm) is dispersed each between the positiveelectrode active material 52 and AB53, AB53 and AB53, aluminum foil 51and the positive electrode active material 52, and the aluminum foil 51and AB53. Moreover, since the graphene-like graphite 54 is in a planarshape and flexible as compared with other materials such as the aluminumfoil 51, the positive electrode active material 52, and AB53, it isconsidered that the aluminum foil 51, the positive electrode activematerial 52, and AB53 are brought into a close contact with each othervia the graphene-like graphite 54, thus discharging characteristics of apositive electrode is improved. In contrast, in the graphene precursorshaving the Rate (3R) of less than 31% (Comparative example 6-1), it isconsidered that an amount of the graphene-like graphite that isdispersed is too small so that an effect of adding the graphene-likegraphite is not sufficiently exerted.

As the Rate (3R) of the graphene precursors increases to 35% (Example6-2) and 42% (Example 6-3), discharging characteristics and capacity ofthe positive electrode are improved as compared with a case of the Rate(3R) being equal to or lower than that. This is because, it isconsidered that, as compared with a case of the Rate (3R) being 31%(Example 6-1), the number and a contact area of the graphene-likegraphite 54, which brings the aluminum foil 51, the positive electrodeactive material 52, and AB53 into a contact with each other, areincreased.

Further, because the graphene precursors are produced by a radiowaveforce-based treatment and/or a physical force-based treatment asdescribed above, it is not necessary to perform an oxidation/reductiontreatment. Further, because a reduction treatment is not necessary toproduce a positive electrode, high temperature is not required, thus apositive electrode is readily produced. In addition, a positiveelectrode is produced under the kneading conditions 1 and 2 as well asby vacuum drying, thus the production thereof is simple.

Further, before being kneaded into the positive electrode activematerials 52, a dispersion in which the graphene-like graphite isdispersed under the dispersion condition 1 is kneaded into AB53, thusthe graphene-like graphite 54 and AB53 are mixed well by the kneadingcondition 1. The mixture is then kneaded into the positive electrodeactive materials 52, so that the graphene-like graphite 54 is disperseduniformly.

It should be noted that, in the dispersion obtained in Step 1, materialsexfoliated from the graphene precursors are dispersed. As describedabove, a part or whole of the graphene precursors is exfoliated toproduce a mixed material containing material from the grapheneprecursors to the graphene, which is referred to as “graphene-likegraphite”. The graphene-like graphite dispersed in the dispersion is notillustrated, however, it can be observed by a transmission electronmicroscope (TEM) in the same manner as the graphene shown in FIG. 10.

For reference, an explanation is given on photographed images of thegraphene precursors taken by a scanning electron microscope (SEM). Thegraphene precursors obtained in Example 1 are a laminate of flakygraphite having a length of 7 μm and a thickness of 0.1 pat as shown forexample in FIGS. 22 and 23.

Example 7

Experiments were performed to obtain a positive electrode of alithium-ion secondary battery using the graphene precursors produced inthe above methods.

In Example 7, carbon nanotubes were used as a conductive material andthe experiments were performed with a mixture ratio in Table 6. The restis the same as in Example 6.

<Various Conditions>

Carbon nanotube: VGCF-H manufactured by Showa Denko K.K. (fiber diameterof 150 nm, fiber length of 10 to 20 μm)

TABLE 6 Mixture ratio (wt %) Graphene precursor Rate (3R) = Rate (3R) =Rate (3R) = Rate (3R) = NCM VGCF-H PVdF 23% (Sample 1) 31% (Sample 2)35% (Sample 21) 42% (Sample 4) Example 7-1 94 3 2 — 1 — — Example 7-2 943 2 — — 1 — Example 7-3 94 3 2 — — — 1 Comparative 94 3 2 1 — — —example 7-1 Comparative 95 3 2 — — — — example 7-2

As shown in FIG. 24, a similar tendency to Example 6 was observed. Byusing the carbon nanotubes, charging and discharging characteristics wasslightly improved overall compared with a case of using AB.

Example 8

Experiments were performed to obtain a positive electrode of alithium-ion secondary battery using the graphene precursors produced inthe above methods.

In Example 8, a mixture ratio of the graphene precursors having the Rate(3R) of 31% to conductive materials was changed under conditions shownin Table 7 to perform experiments. The rest is the same as in Example 6.

TABLE 7 Mixture ratio (wt %) Graphene precursor Rate (3R) = 31% NCM ABPVdF (Sample 2) Example 6-1 94 3 2 1 Example 8-1 93 3 2 2 Example 8-2 923 2 3 Example 8-3 91 3 2 4 Example 8-4 90 3 2 5 Example 8-5 94.5 3 2 0.5Example 8-6 94.9 3 2 0.1 Example 8-7 94.95 3 2 0.05 Comparative 95 3 2 —example 6-2

As shown in FIG. 25, when the mixture ratio of the graphene precursorsto the conductive materials is greater than 1 (Example 8-2), a mostlysimilar trend in charging and discharging characteristics was observed,showing that the characteristics was saturated. Further, when themixture ratio of the graphene precursors was 10 or more, an impact onproperties of base materials becomes significant. On the other hand,when the mixture ratio was less than 1/50 (Example 8-7), a mostlysimilar trend was observed to a case where the graphene precursors werenot mixed (Comparative example 6-2), and when the mixture ratio was 1/10or more (Example 8-6), improvement of charging and dischargingcharacteristics was observed. Based on these, a lower limit of themixture ratio is 1/50 or more, preferably 1/10 or more, and an upperlimit thereof is 10 or less, preferably 1 or less.

Example 9

Next, experiments were performed to obtain a resin molded article usingthe graphene precursors produced in the above methods.

<Various Conditions> <<Materials>>

Resin: LLDPE (polyethylene: 20201) manufactured by Prime Polymer Co.,Ltd.),

Solvent: Water (ion exchange water),

Dispersant: 1 wt % (nonionic surfactant),

Ultrasonic treatment device (UP100S manufactured by HielscherUltrasonics GmbH),

-   -   <Treatment condition: 20 kHz, 100 W>    -   <Dispersion condition 2: Graphene precursors are mixed with ion        exchange water together with 1 wt % of a dispersant (nonionic        surfactant), and the mixture was processed with the        aforementioned device shown in FIG. 8 operated under the same        condition to obtain a dispersion having 10 wt % of graphene-like        graphite.>

<<Kneader>>

Kneader: Pressing-type kneader WDS7-30 manufactured by Moriyama Co.,Ltd.,

-   -   Kneading temperature: 135° C.,    -   Rotor rotation speed: 30 r/min,    -   Processing time: 15 min,    -   Mixture ratio: Resin 5,340 g, AB (HS-100) 600 g, dispersion 600        g (60 g in terms of graphene-like graphite),

<<Volume Resistance Value>>

Test piece: ø100 mm×t3 mm (ASTM D257),

Measuring device: Device body (R-503 manufactured by Kawaguchi ElectricWorks Co., Ltd), electrode device (P-616 manufactured by KawaguchiElectric Works Co., Ltd),

-   -   Applied voltage: 500 V,    -   Electric current is measured 1 min after applying voltage,

<<Thermal Conductivity>>

Test ø50 mm×t3 mm (ASTM E1530),

Measuring device: UNITHERM 2021 manufactured by ANTER Corp.

Experimental Procedures

Step 1. By using graphene precursors having a different Rate (3R) asshown in Table 8, a dispersion is obtained under the dispersioncondition 2.Step 2. The dispersion obtained in Step 1 and a resin are placed in apressing-type kneader and kneaded with a mixture ratio described above.Step 3. A kneaded mixture obtained in Step 2 was formed into a testpiece according to ASTM D257 by an injection molding machine and changesin volume resistance values were observed.Step 4. A kneaded mixture obtained in Step 2 was formed into a testpiece according to ASTM E1530 by an injection molding machine, andchanges in thermal conductivity were observed by a regular method.

TABLE 8 Mixture ratio (wt %) Graphene precursor Volume Thermal Rate (3R)= Rate (3R) = Rate (3R) = Rate (3R) = resistance conductivity LLDPE AB23% (Sample 1) 31% (Sample 2) 35% (Sample 21) 42% (Sample 4) (Ωcm)(W/mK) Example 9-1 89 10 — 1 — — 8.9 × 10⁶  5.2 Example 9-2 89 10 — — 1— 5.5 × 10⁶  5.7 Example 9-3 89 10 — — 1 3.4 × 10⁶  6.8 Comparative 8910 1 — — — 3.0 × 10¹⁰ 1.2 example 9-1 Comparative 90 10 — — — — 2.7 ×10¹⁰ 1.1 example 9-2 Comparative 99 — — 1 — — 7.8 × 10¹⁷ 0.4 example 9-3Comparative 100 — — — — — 5.4 × 10¹⁸ 0.32 example 9-4

From Table 8, Examples 9-1, 9-2, and 9-3, all have low volume resistanceand are excellent in electrical conductivity.

Further it was observed that thermal conductivity was significantlyhigher in Examples 9-1, 9-2, and 9-3 than in Comparative examples 9-1,9-2, 9-3, and 9-4.

When the graphene-like graphite exfoliated from the graphene precursorshaving the Rate (3R) of 31% or more (Examples 9-1, 9-2, and 9-3) wasused together with AB, it was confirmed that volume resistance andthermal conductivity were improved. Especially, from Table 8, it wasconfirmed that the volume resistance and the thermal conductivity showeda tendency to improve sharply after the Rate (3R) reached 31%. It isconsidered that this is due to the following reasons: according to thesame principle as in Example 6, AB having a cross sectional diameter ofseveral hundreds of nm to several exists between high molecules ofLLDPE. It is speculated that the graphene-like graphite is dispersedeach between LLDPE and AB, AB and AB, and LLDPE and LLDPE. Since thegraphene-like graphite is in a planar shape and flexible as comparedwith other materials such as LLDPE and AB, it is considered that LLDPEand AB are brought into a close contact with each other via thegraphene-like graphite, thus the volume resistance and the thermalconductivity are improved. In contrast, when the Rate (3R) is less than31% (Comparative example 9-1), it is considered that an amount of thegraphene-like graphite that is dispersed is too small so that an effectof dispersing the graphene-like graphite is not sufficiently exerted.

As the Rate (3R) increases to 35% (Example 9-2) and 42% (Example 9-3),the volume resistance and the thermal conductivity are improved ascompared with a case of the Rate (3R) being equal to or lower than that.This is because, it is considered that, as compared with a case of theRate (3R) being 31% (Example 9-1), the number and a contact area of thegraphene-like graphite, which brings LLDPE and AB into a contact witheach other, are increased.

It should be noted that, in the dispersion obtained in Step 1, materialsexfoliated from the graphene precursors are dispersed. As describedabove, apart or whole of the graphene precursors is exfoliated toproduce a mixed material containing material from the grapheneprecursors to the graphene, which is referred to as “graphene-likegraphite”. The graphene-like graphite dispersed in the dispersion is notillustrated, however, they can be observed by a transmission electronmicroscope (TEM) in the same manner as the graphene shown in FIG. 10.

Further, the graphene-like graphite dispersed in a resin can be observedby a scanning electron microscope (SEM) and the like after being formedinto a test piece and cut by a precision high-speed saw (TechCut5manufactured by Allied High Tech Products, Inc.) and the like. Forexample, FIG. 26 shows a cross section of a resin in which carbonnanotubes and graphene-like graphite are dispersed, where the carbonnanotubes are represented by linear parts and the graphene-like graphiteis represented by white spotted parts. This graphene-like graphite is alaminate of flaky graphite having a thickness of 3.97 nm as shown forexample in FIG. 27.

Example 10

Next, experiments were performed to obtain a resin molded article usingthe graphene precursors produced in the above methods.

The experiments were performed with a mixture ratio of the grapheneprecursors having the Rate (3R) of 31% to conductive materials underconditions shown in Table 9.

<Various Conditions> <<Materials>>

Resin: LLDPE (polyethylene: 20201) manufactured by Prime Polymer Co.,Ltd.),

Compatibilizer: KAYABRID 006PP (maleic anhydride-modified PPmanufactured by Kayaku Akzo Corp.),

Acetylene black (HS-100 manufactured by Denki Kagaku Kogyo KabushikiKaisha, average particle diameter of 48 nm, bulk density of 0.15 g/ml,ash content of 0.01%),

<<Two-Shaft Extruder>>

Two-shaft extruder: HYPERKTX 30 manufactured by Kobe Steel, Ltd.,

-   -   Kneading temperature: 135° C.,    -   Screw rotation speed: 100 r/min,

<<Volume Resistance Value>>

Test piece: ø100 mm×t3 mm (ASTM D257),

Measuring device: Device body (R-503 manufactured by Kawaguchi ElectricWorks Co., Ltd), electrode device (P-616 manufactured by KawaguchiElectric Works Co., Ltd),

Applied voltage: 500 V,

Electric current is measured 1 min after applying voltage,

<<Thermal Conductivity>>

Test piece: ø50 mm×t3 mm (ASTM E1530),

Measuring device: UNITHERM 2021 manufactured by ANTER Corp.

Experimental Procedures

Step 1. Graphene precursors having a different Rate (3R) as shown inTable 9 and a compatibilizer are kneaded by a two-shaft extruder toobtain a mixture 1 containing 40 wt % of graphene-like graphite. Itshould be noted that graphene precursors become graphene-like graphiteduring the process of kneading.Step 2. In the same two-shaft extruder, the mixture 1 obtained in Step1, a resin, and AB are kneaded with a mixture ratio shown in Table 9.Step 3. A kneaded mixture obtained in Step 2 was formed into a testpiece according to ASTM D257 by an injection molding machine and changesin volume resistance values were observed.Step 4. The kneaded mixture obtained in Step 2 was formed into a testpiece according to ASTM E1530 by an injection molding machine andchanges in the thermal conductivity were observed by a regular method.

It should be noted that the volume resistance and the thermalconductivity caused by the compatibilizer are not significantlydifferent from those of the resin serving as a base material, thus theyshall not be considered in the present embodiments.

TABLE 9 Mixture ratio(wt %) Graphene precursor Volume Thermal LLDPE Rate(3R) = 31% resistance conductivity (compatibilizer) AB (Sample 2) (Ωcm)(W/mK) Example 10-1  89 (1.5) 10 1 9.5 × 10⁶ 5.3 Example 10-2  87 (4.5)10 3 1.5 × 10⁶ 5.9 Example 10-3  85 (7.5) 10 5 4.2 × 10⁵ 6.2 Example10-4 82 (12) 10 8 1.5 × 10⁵ 6.8 Example 10-5 80 (15) 10 10 9.8 × 10⁴ 7.0Example 10-6   75 (22.5) 10 15 9.2 × 10⁴ 7.1 Example 10-7 89.5 (0.75) 100.5 8.9 × 10⁷ 3.1 Comparative 89.7 (0.45) 10 0.3 5.6 × 10⁹ 2.0 example10-8 Comparative 89.9 (0.15) 10 0.1 2.5 × 10¹⁰ 1.3 example 10-9Comparative 90 (0)  10 — 2.7 × 10¹⁰ 1.1 example 9-2 Comparative 100 (0) — — 5.4 × 10¹⁸ 0.32 example 9-4 Comparative 100 (25)  — — 5.5 × 10¹⁸0.31 example 10-10

As shown in Table 9, when the mixture ratio of the graphene precursorsto the conductive materials was greater than 1 (Example 10-5), it wasobserved that the volume resistance and the thermal conductivity stayedat mostly the same values and their characteristics became saturated.Further, when the mixture ratio of the graphene precursors is 10 ormore, an impact on properties of base materials becomes significant. Onthe other hand, when the mixture ratio was less than 1/50 (Comparativeexample 10-9), it was observed that the volume resistance and thethermal conductivity were mostly the same as a case where the grapheneprecursors were not mixed (Comparative example 9-2). Based on these, alower limit of the mixture ratio is 1/50 or more, preferably 1/10 ormore, and an upper limit thereof is 10 or less, preferably 1 or less.

Example 11

Next, experiments were performed to obtain a resin molded article usingthe graphene precursors produced in the above methods.

In Example 11, a conductive material used for mixing with the grapheneprecursors having the Rate (3R) of 31% was changed and an effect causedby a shape of the conductive material was confirmed. The rest is thesame as in Example 9.

As shown in FIG. 28, acetylene black (AB), a type of carbon black,serving as a conductive material, is a string-like or a straightchain-like shape, having a diameter of several tens of nm and a lengthof several to several tens of μm. Carbon fibers (CF) have a linear shapehaving a diameter of several tens of μm and a length of several hundredsof μm. Metallic particles have a diameter of several tens of nm toseveral μm.

TABLE 10 Mixture ratio (wt %) Graphene precursor Volume Thermal MetallicRate (3R) = resistance conductivity LLDPE AB CF nanoparticle 31% (Sample2) (Ωcm) (W/mK) Example 9-1 89 10 — — 1 8.9 × 10⁶  5.2 Example 11-1 89 —10 — 1 4.5 × 10⁴  7.5 Example 11-2 89 — — 10 1 7.5 × 10¹⁵ 0.85Comparative 90 10 — — — 2.7 × 10¹⁰ 1.1 example 9-2 Comparative 90 — 10 —— 5.2 × 10⁸  2.2 example 11-1 Comparative 90 — — 10 — 4.8 × 10¹⁶ 0.41example 11-2 Comparative 100 — — — — 5.4 × 10¹⁸ 0.32 example 9-4

As shown in Table 10, both Example 9-1 where AB was added and Example11-1 where CF was added were excellent in the volume resistance and thethermal conductivity. In contrast, Example 11-2 where metallic particleswere added did not show excellent volume resistance or thermalconductivity although the graphene precursors were added and thegraphene-like graphite was dispersed. Based on these, it was found thata graphene precursor was preferably used together with a conductivematerial having a string-like, a straight chain-like, or a linear shape.Further, although not shown in examples, a conductive material having aflake-like shape was also excellent in the volume resistance and thethermal conductivity. Since a nano conductive material in a string-like,a straight chain-like, a linear, or a flake-like shape has a widesurface area per unit mass because of its shape, it is speculated thatit is brought into a contact with many pieces of graphene-like graphite,thus having high compatibility with the graphene-like graphite. It wasalso revealed that, as a conductive material in a string-like, astraight chain-like, a linear, or a flake-like shape, having an aspectratio of 5 or mere is particularly preferable. It is noted that anaspect ratio of a material having a branched structure such as acetyleneblack may be obtained by calculating a ratio of an average diameter to alength of the longest part. Further, an aspect ratio of a material in aflake-like shape may be obtained by calculating a ratio of an averagethickness to a length of the longest part.

Example 12

Next, experiments were performed to obtain a resin molded article usingthe graphene precursors produced in the above methods. In Example 12,the experiments were performed using a graphene paste produced fromgraphene precursors under the dispersion condition 3.

<Various Conditions> <Materials>

Diacetone alcohol: Manufactured by Wako Pure Chemical Industries,

Methylparaben: Manufactured by Wako Pure Chemical Industries,

Stabilizer: Nitrocellulose DLX-30-50 (Nobel NC Co. Ltd),

Acetylene black (HS-100 manufactured by Denki Kagaku Kogyo KabushikiKaisha, average particle diameter of 48 nm, bulk density of 0.15 g/ml,ash content of 0.01%),

<Mixing>

Mixer (ARE-310 manufactured by THINKY),

-   -   <Mixing condition 3>: Normal temperature of 25° C., mixing at        2,000 rpm×10 min, defoaming after mixing at 2,100 rpm×30 sec)

<Coating Condition 1>

Bar coater: No. 16 manufactured by Dai-Ichi Rika Co., Ltd.,

Coating film thickness: 36.6 μm (25.4 μm after drying),

Drying condition: 130° C.×30 min,

Substrate: quartz glass (t2 mm),

Coating area: 50 mm×50 mm,

<Sheet Resistance Measuring Instrument>,

LorestaGP MCP-T610 type manufactured by Mitsubishi Chemical AnalytechCo., Ltd.,

Measuring condition: JIS K7194

Experimental Procedures

Step 1. Graphene precursors having a different Rate (3R) as shown inTable 11 are added to diacetone alcohol(4-hydroxy-4-methyl-2-pentanone), and the mixture is processed with theaforementioned device shown in FIG. 8 operated under the same drivingcondition to obtain a dispersion having 10 wt % of graphene-likegraphite. (the dispersion condition 3)Step 2. The graphene dispersion obtained in Step 1, methylparaben(methyl 4-hydroxybenzoate), a stabilizer, and AB are added at a ratioshown in Table 11 and mixed under the mixing condition 3 to obtain amixture 3.Step 3. The mixture 3 is coated using a bar coater under the coatingcondition 1 and sheet resistance is measured according to JIS K7194 by afour probe method.

TABLE 11 Mixture ratio (wt %) Di- Graphene precursor Sheet acetoneMethyl Rate (3R) = Rate (3R) = Rate (3R) = Rate (3R) = resistancealcohol paraben Stabilizer AB 23% (Sample 1) 31% (Sample 2) 35% (Sample21) 42% (Sample 4) (Ω/sq) Example 12-1 25 20 15 30 — 10 — 22 Example12-2 25 20 15 30 10 15 Example 12-3 25 20 15 30 — — 10 8 Comparative 2520 15 30 10 — — 54 example 12-1 Comparative 25 20 15 40 — — — 56 example12-2

As shown in Table 11, it was observed that Examples 12-1, 12-2, and 12-3had lower sheet resistance than Comparative examples 12-1 and 12-2. Itwas also observed that Comparative example 12-1 having the Rate (3R) of23% had substantially the same sheet resistance as Comparative example12-2 where the graphene precursors were not added. Based on these, it isspeculated that, in Examples 12-1, 12-2, and 12-3, the graphene-likegraphite together with AB significantly contribute to lowering the sheetresistance. Further it was found that the graphene paste prepared byusing the graphene precursors having the Rate (3R) of 31% or more(Examples 12-1, 12-2, and 12-3) sharply reduced the sheet resistance ascompared with the graphene paste prepared by using the one having theRate (3R) of 23% (Comparative example 12-1).

It should be noted that, in the present embodiments, only basicmaterials were used for constitution in order to exclude disturbancefactors. In a conductive ink and paste for practical an antioxidant, aviscosity modifier, and a plurality of conductive materials are normallyadded for providing a desired ink and lowering a resistance value.

The foregoing explained the embodiments of the present invention usingdrawings, however it should be understood that the specificconstitutions are not at all restricted to these embodiments, andchanges and additions are also included in the present invention withoutdeparting from the gist of the present invention.

In the aforementioned embodiments, the production apparatus A using ajet mill and plasma and the production apparatus B using a ball mill andmicrowaves are described as a production apparatus which produces agraphene precursor. When a treatment based on a radiowave force such asby microwaves, millimeter waves, plasma, electromagnetic inductionheating (IH), and magnetic fields, and a treatment based on a physicalforce such as by a ball mill, a jet mill, centrifugal force, andsupercriticality are combined for use, a precursor having a high Rate(R3) can be obtained. Therefore, such combination of the treatments ispreferable. Additionally, as long as the radiowave force-basedtreatments and the physical force-based treatments are used incombination, there is no restriction on a specific kind of the radiowaveforce-based treatments or the physical force-based treatments to beapplied. In particular, as exemplified in the production apparatuses Aand B, it is preferable that effects based on the radiowave force andthe physical force are simultaneously exerted. However, the radiowaveforce and the physical force may be alternately exerted at predeterminedintervals. Moreover, as for the radiowave force, different radiowaveforces, such as treatments based on microwaves and plasma, may bealternately exerted, and, in parallel with the treatments, one or moretreatments based on the physical forces may be exerted. Conversely, asfor the physical force, different physical forces, such as treatmentsbased on a jet mill and supercriticality, may be alternately exerted,and, in parallel with the treatments, one or more treatments based onthe radiowave forces may be exerted.

As examples of base materials for dispersing conductive materials andgraphite-based carbon materials, the following materials can bementioned. It is noted that a ratio of base materials may be smallerthan that of conductive materials or graphite-based carbon materials.Further, base materials may be annihilated by combustion, oxidation,vaporization, evaporation, and the like when in use. For example, basematerials will be annihilated from a conductive paste, a conductive ink,etc., where the base materials are volatile solvents and the like. Easematerials may additionally include a conductive material.

Examples of positive electrode active materials include layeredoxide-based active materials (LiCoO₂, LiNiO₂, Li(Ni_(x)Co_(y))O₂(wherein x+y=1), Li(Ni_(x)Co_(y)Al_(z))O₂, Li(Ni_(x)Mn_(y)Co_(z))O₂,Li(Ni_(x)Mn_(y))O₂, Li₂MnO₃—Li(Ni_(x)Mn_(y)Co_(z))O₂ (wherein x+y+z=1),etc.), olivine-based active materials (LiMPO₄, Li₂MPO₄F, Li₂MSiO₄(wherein each M denotes one or more kinds of metallic elements selectedfrom Ni, Co, Fe, and Mn)), Lithium-rich active materials, spinel typepositive electrode active materials (LiMn₂O₄), and the like.

Examples of resins include thermoplastic resins such as polyethylene(PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC),ABS resins (ABS), acrylic resins (PMMA), polyamide/nylon (PA),polyacetal (POM), polycarbonate (PC), polyethylene terephthalate (PET),cyclic polyolefins (COP), polyphenylene sulfide (PPS),polytetrafluoroethylene (PTFE), polysulfone (PSF), polyamide-imide(PAI), thermoplastic polyimide (PI), polyether ether ketone (PEEK), andliquid-crystal polymers (LCP). In addition, among synthetic resins: asthermosetting resins or ultraviolet curing resins, included are epoxyresins (EP), phenolic resins (PF), melamine resins (MF), polyurethanes(PUR), and unsaturated polyester resins (UP) and the like; as conductivepolymers, included are PEDOT, polythiophene, polyacetylene, polyaniline,polypyrrole, and the like; as fibers, included are fibrous nylon,polyesters, acryl, vinylon, polyolefin, polyurethane, rayon and thelike; as elastomers, included are isoprene rubbers (IR), butadienerubbers (BR), styrene/butadiene rubbers (SBR), chloroprene rubbers (CR),nitrile rubbers (NBR), polyisobutylene rubbers/butyl rubbers (IIR),ethylene propylene rubbers (EPM/EPDM), chlorosulfonated polyethylene(CSM), acrylic rubbers (ACM), epichlorohydrin rubbers (CO/ECO), and thelike; as thermosetting resin-based elastomers, included are someurethane rubbers (U), silicone rubbers (Q), fluorine-containing rubbers(FKM), and the like; and, as thermoplastic elastomers, included areelastomers based on styrene, olefin, polyvinyl chloride, urethane, andamide.

Moreover, as mineral oils, included are lubricating oils, and greases,and, as compounded oils for rubbers, included are paraffin-based mineraloils, naphthenic mineral oil, aromatic mineral oils, and the like.

Furthermore, as nonpolar products, included are hexane, benzene,toluene, chloroform, ethyl acetate, and the like, as polar aproticproducts, included are acetone, N,N-dimethylformamide (DMF),N-methylpyrrolidone (NMP), acetonitrile, and the like, and, as polarprotic products, included are acetic acid, ethanol, methanol, water,1-butanol, 2-propanol, formic acid, and the like.

As conductive materials, the followings can be mentioned. As metallicmaterials, included are silver nanoparticles, copper nanoparticles,silver nanowires, copper nanowires, flaky silver, flaky copper, ironpowders, zinc oxide, and the like. As carbon materials, included arecarbon black, carbon fibers, CNT, graphite, activated carbon, and thelike. As conductive polymers, included are PEDOT, polythiophene,polyacetylene, polyaniline, polypyrrole, and the like. In particular,fibrous materials in a chain-like, string-like, and flake-like shape areexcellent in conductivity.

Further, as an example of natural graphite for producing agraphite-based carbon material useful as a graphene precursor, a naturalgraphite material in a particulate shape having a size of 5 mm or less(flaky graphite ACB-50 manufactured by Nippon Graphite Industries, Ltd.)is described above. As for natural graphite, a preferable product isflaky graphite that is pulverized into 5 mm or less, having a Rate (3R)of less than 25% and an intensity ratio P1/P2 of less than 0.01, from aperspective of being easily procured. Corresponding to recent technologydevelopment, natural graphite-like graphite (in which crystals arestacked in layers) can be artificially synthesized, thus raw materialsfor graphene and graphene-like graphite are not limited to naturalgraphite (mineral). Artificial graphite having a high degree of purityis preferably used for a purpose of controlling a metal content such asin a battery.

It should be noted that a graphite-based carbon material useful as agraphene precursor is generally referred to as graphene, a grapheneprecursor, a graphene nanoplatelet (GNP), few-layer graphene (FLG),nanographene, and the like, however it is not particularly limitedthereto.

INDUSTRIAL APPLICABILITY

The present invention covers a composite conductive material havingconductivity, and an application field thereof is not limited. It shouldbe noted that, in the present invention, conductivity refers to at leastone of electrical conductivity, ion conductivity, and thermalconductivity. The following fields are included as examples.

(1) Examples of Electrical Conductors (Conductors) (1-1) Power StorageDevice (1-1-1) Battery

Included are electrical conductive materials used for a positiveelectrode material, a negative electrode material and the like for abattery, in particular a lithium-ion battery, the electrical conductivematerials being preferably excellent in both electrical conductivity andion conductivity. As a material constituting a battery, the followingmaterials are exemplified, however, it is not limited thereto.

Positive electrode active material: LiCoO₂, LiMn₂O₄, LiNiO₂, LiFeO₄,Li₂FePO₄F, Li(Co_(x),Ni_(y),Mn_(z))O₂

Conductive assistant: graphite powders, acetylene black, VGCF, CNT

Negative electrode material: graphite powders, hard carbon, activatedcarbon, titanate (Li₄Ti₅O₁₂), Si

Electrolyte solution: PC (polycarbonate), EC (ethylene carbonate), DEC(diethyl carbonate)

Supporting electrolyte: LiPF₆, LiBF₄, LiTFSI

Collecting conductor: aluminum foil, copper foil, lithium foil

(1-1-2) Capacitor and Condenser

Included are capacitors and condensers, such as a lithium-ion capacitor,an electric double-layered capacitor, and a condenser, preferablyexcellent in electrical conductivity. As a material constitutingcapacitors and condensers, the following materials are exemplified,however, it is not limited thereto.

Collecting electrode: aluminum foil

Polarizable electrode: activated carbon

Conductive assistant: carbon black, CNT

Electrolyte: tetraethylammonium ion, tetrafluoroborate ion,bis(trifluoromethylsulfonyl)imide

Electrolyte solution: propylene carbonate, ethylene carbonate, diethylcarbonate, dimethyl carbonate

(1-2) Conductive Dispersion

Included are conductive dispersions, such as a conductive ink, aconductive paste, a conductive slurry, and the like, used for conductivedevices that include a transparent/non-transparent conductive film andan electronic circuit substrate (printing and photo-etching), theconductive dispersions being preferably excellent in electricalconductivity. As a material constituting conductive dispersions, thefollowing materials are exemplified, however, it is not limited thereto.

Solvent: water, drying preventing agents (glycerin, glycols, etc.),penetrants (alcohols, glycol ethers, etc.), alcohols, NMP(N-methylpyrrolidone), DMF, toluene, ethyl acetoacetate, ketones

Colorant: dyes, pigments

Resin: thermoplastics resins such as acrylic block copolymers, acryl,maleic acid, rosin, epoxy, silicones, butyral, and the like

Additive: pH regulators, chelating agents, surfactants, antibacterialand antifungal agents, antioxidants, ultraviolet absorbing agents,plasticizers

Conductive material: graphite powders, carbon black (Ketjen black,acetylene black, etc.), carbon fibers, CNT (SWNT and MWNT), metal finepowders (copper/silver nanoparticles), metal oxides (ITO and zincoxide), metal fibers (copper/silver nanowires), conductive polymers(PEDOT, polyacetylene, etc.)

(1-3) Conductive Composite

Included are conductive composites such as for use in preventingconductivity, static electricity, and electrification, and interceptingelectromagnetic waves, the conductive composites being preferablyexcellent in electrical conductivity. As a material constitutingconductive composites, the following materials are exemplified, however,it is not limited thereto.

Electrical conductive material: Fe and Ni as metal. Carbon fibers,isotropic graphite, and carbon black as carbon materials.

Polymer: PE, PP, PS, PC, PVC, ABS, PA6, PA66, PSS, PEEK, POM, epoxy,natural rubbers, chloroprene rubbers, NBR, silicone rubbers.

(2) Examples of Thermal Conductivity (2-1) Thermally ConductiveComposite (2-1-1) Heat Sinks for Thermal Conductive Films, ThermalConductive Polymers, Etc.

Included are heat sinks capable of improving heat resistance time of amixture by releasing local heat, preferably excellent in thermalconductivity. As a material constituting heat sinks, the followingmaterials are exemplified, however, it is not limited thereto.

Conductive material: Cu, Al, and W as metal. Carbon fibers and isotropicgraphite as carbon materials.

Polymer: PE, PP, PS, PC, PVC, ABS, PA6, PA66, PSS, PEEK, POM, epoxy,natural rubbers, chloroprene rubbers, NBR, silicone rubbers.

(2-1-2) Heat Radiation Grease and Paste

Included are a heat radiation grease and paste serving as a material forconnecting between a heat radiation object and a heat sink asexemplified in (2-1-1), preferably excellent in thermal conductivity. Asa material constituting a heat radiation grease and paste, the followingmaterials are exemplified, however, it is not limited thereto.

Solvent: silicone grease (polysiloxane compounds)

Conducting agents: zinc oxide, silver nanoparticles, nanodiamond, carbonblack, silicon nanoparticles

REFERENCE SIGNS LIST

-   51 An aluminum foil-   52 A positive electrode active material (base material)-   53 AB (conductive material)-   54 Graphene-like graphite

1: A composite conductive material comprising at least graphene-likegraphite exfoliated from a graphite-based carbon material and aconductive material dispersed in a base material, the graphite-basedcarbon material having, just before exfoliation of the graphene-likegraphite from the graphite-based carbon material, a rhombohedralgraphite layer (3R) and a hexagonal graphite layer (2H), wherein a Rate(3R) of the rhombohedral graphite layer (3R) and the hexagonal graphitelayer (2H), based on an X-ray diffraction method, which is defined byfollowing Equation 1, is 31% or more:Rate (3R)=P3/(P3+P4)×100  (Equation 1) wherein P3 is a peak intensity ofa (101) plane of the rhombohedral graphite layer (3R) based on the X-raydiffraction method, P4 is a peak intensity of a (101) plane of thehexagonal graphite layer (2H) based on the X-ray diffraction method, thegraphene-like graphite being a mixed material containing at leastgraphene produced by exfoliating a part or whole of the graphite-basedthe graphene being a crystal of a mean size of 100 nm or more and formedin a flake-like or sheet-like shape having 10 layers or less. 2: Thecomposite conductive material according to claim 1, wherein theconductive material is a microparticle in a string-like, straightchain-like, linear, or flake-like shape. 3: The composite conductivematerial according to claim 2, wherein the microparticle has an aspectratio of 5 or more. 4: The composite conductive material according toclaim 1, wherein a weight ratio of the graphite-based carbon material tothe conductive material is 1/50 or more and less than 10/1. 5: Thecomposite conductive material according to claim 1, wherein the basematerial is an active material for a battery. 6: The compositeconductive material according to claim 5, wherein the active material isa positive electrode active material. 7: The composite conductivematerial according to claim 1, wherein the base material is a polymer.8: The composite conductive material according to claim 1, wherein thebase material is a material that is annihilated when in use. 9: A powerstorage device—comprising the composite conductive material according toclaim
 1. 10: A conductive dispersion comprising the composite conductivematerial according to claim
 1. 11: A conductive device, such as atransparent electrode, a transparent conductive film, a conductivecircuit, or a substrate, being coated or printed using the conductivedispersion according to claim
 10. 12: A conductive composite comprisingthe composite conductive material according to claim
 1. 13: A thermalconductive composite-comprising the composite conductive materialaccording to claim
 1. 14.-18. (canceled) 19: The composite conductivematerial according to claim 2, wherein a weight ratio of thegraphite-based carbon material to the conductive material is 1/50 ormore and less than 10/1.